Endothelial dysfunction, or abnormal functioning of the lining of blood vessels, appears to be a key process in the development of cardiovascular disease. Endothelial dysfunction appears to be caused by both sleep disordered breathing and obesity. As endothelial dysfunction is among the first clinical marker that predicts future cardiovascular events, understanding molecular mechanisms leading to impairment of endothelial function is very important. Endothelial function requires the proper functioning of endothelial nitric oxide synthase (eNOS). eNOS activity is tightly regulated by caveolin-1, a protein important in the formation of cellular structures called caveolae. Low levels of caveolin-1 facilitate optimal nitric oxide synthesis in endothelial cells as caveolin-1 helps to spatially organize eNOS in close proximity to signaling proteins that are important for eNOS activation. In certain diseases however, the balance of caveolin-1 and eNOS can be disrupted resulting in impaired nitric oxide synthesis and leading to endothelial dysfunction.